DYNAMIC STRATIGRAPHY WORKGROUP

Summary of work:

This research project approached the problem of sediment partitioning along a regional transect in the Cretaceous Western Interior Basin. The rock succession studied in this project corresponds to a 3rd-order regressive-transgressive clastic wedge that was deposited in the Cretaceous Western Interior Seaway, located in south Wyoming and north Colorado. This wedge spans the time slice between ammonite zones Baculites perplexus complex to Exiteloceras jenneyi. In the proximal parts of the system the Campanian Trail and Rusty members of the Ericson Sandstone in southwest Wyoming were studied. Moving to the southeast, the intermediate (shoreline) reaches were studied using the coeval Iles Wedge in the Sand Wash Basin. Finally, the distal zone of the system was studied in the time-equivalent Muddy Buttes-Hygiene-Carter and Hygiene-Terry Sandstones in the Middle Park and Denver Basins. The ca. 3 m.y. stratigraphic time slice was studied using outcrop and subsurface data to create an integrated regional (400 km) transect running from southwest Wyoming to north-central Colorado.

 

Quantification of the amounts of sediment differentially sequestered during one complete cycle of relative sea level fall & rise at both 4th and 3rd order time scales was based on a working hypothesis that during early and main stages of relative sea level fall, erosion and sediment bypass occur throughout the upstream or fluvial part of the system, whereas widespread progradation and deposition occurs from the shoreline out into the basin. During sea level rise and transgression, however, almost the opposite happens, i.e., there is transgressive erosion and minimal deposition across the new marine shelf but significant sediment sequestering in the most proximal parts of the system, i.e. in the estuarine/coastal plain and fluvial areas. The falling-stage, however, is controversial and other models anticipate less widespread erosion and partial filling of incised valleys during falling relative sea level, so that the sediment budget is partitioned both proximally and distally during regression.

 

The roles of Laramide (local) and Sevier (regional) tectonics in the proximal parts of the system were investigated to elucidate whether it has a 3rd-order or 4th-order timescale impact. Isopach and facies maps of the proximal reaches of the system (Trail, Rusty, and Trail plus Rusty members) were constructed and the geometries and lateral thickness changes of component 4th order cycles were assessed.

 

Publications and presentations: 

Publications:

 

Conference/meeting presentations:

Gomez, C., Steel, R., 2008. The Iles Clastic Wedge in the Sand Wash Basin: high-frequency sequences and shoreline processes within the wedge. AAPG Meeting (San Antonio, Texas), Abstract.

Gomez, C., Steel, R., 2007. Tidal channel to bay-head delta couplets: key to 4th order proximal sequence identification and correlation, Upper Iles Formation, Colorado. AAPG Meeting (Long Beach, California), Abstract.

Gomez, C., Steel, R., Peters, A., 2006. Source-to-Sink Sand and Mud Partitioning across a 300 km Transgression of the Western Interior Seaway (Campanian). RMS-AAPG Meeting (Billings, Montana), Abstract.

Martinsen, R., Steel, R., Van Holland, A., Gomez, C., 2005. Regressive vs. transgressive systems: processes & geometries. RMS-AAPG Meeting (Jackson Hole, Wyoming), Field Guidebook.

Gomez, C., Steel, R., 2005. Significance of estuarine valleys in the cores of clastic wedges: Ericson Formation, Wyoming. AAPG Bulletin, Vol. 89, Program Abstracts (Digital).

People:

Carolina Gomez, Ron Steel

 

Research question(s):

The problem of how sand and mud is distributed within sedimentary systems or how the total sediment budget is differentially stored and by-passed along source-to-sink time slices is currently a research topic of significant interest in the Sedimentary Geology community. The topic is important from a purely academic viewpoint (budget partitioning) as well as from an applied one. Another problem related with the sediment budget partitioning is the establishment of the role of local tectonics and regional tectonics in the development of the sequences of various orders described above.

Sediment budget distribution in a source-to-sink transect (Late Campanian Western Interior Basin, SW Wyoming and N Colorado)